1. Field of the Invention
This invention is in the field of acoustic attenuation structures, and in particular applies to broadband noise suppression using mechanically coupled Helmholtz resonators.
2. Description of the Prior Art
Broadband noise suppression is of interest in many areas including but not limited to launch vehicles, aircraft, automotive mufflers, and many common engines and commercial HVAC systems. One traditional approach to noise suppression is the use of Helmholtz resonators. These are carefully sized cavities that can provide excellent noise suppression at a specific frequency. Unfortunately, all of the noise sources described above are broadband and, therefore, must be targeted by noise suppression approaches that suppress acoustics over a wide spectrum of frequencies. Multiple Helmholtz resonators can be used to target such broadband spectrums by tuning each resonator to a different frequency. The acoustic attenuation, however, will still have peaks corresponding to each targeted frequency with valleys in between.
The present invention provides a method to substantially "smooth" out these peaks and valleys. By mechanically coupling multiple Helmholtz resonators, many new degrees of freedom can be added to the system. These degrees of freedom can be used to target additional frequencies between the peaks causing the acoustic attenuation to be significantly more flat, and thereby better targeting broadband acoustic noise.